Air-driven gyroscopic instrument



Aug 14, 1945.

D. CREW 2,382,135

AIR-DRIVEN GYROSCOPIC INSTRUMENT Filed Feb. 25, 1943 Patented Aug. 14, 1945 UNITED STATES PATENT OFFICE-1., T, 72,382,135 I y 4 AIR- DRIVENQGYROSCOPIC INSTRUMENT David. Crew; Kingston By-Pass, New Malden, England, assignor to Reid & SigristLimited, New Malden, Surrey, England Applieationlebruary 25, 1943, Serial No. 477,154 In Great Britain March 2, 1942 2 Claims.

This invention relates to air driven gyroscopic instruments, such as direction indicators, rate of turn indicators, artificial horizons and thelike- It is the primary object of the invention to provide: improvements in such instruments, more especially with a view to increasing the power which isderived from a given current: of air. This is of particular importance ior the gyroscopic instruments of aircraft, for the available air pressure drops seriously as the altitude. increases. It. is. a. further object of the invention to provide an improved fluid packing-tor use between a pair of relatively rotatable parts of an air driven gyroscopic. instrument, the seal having very little working friction.

In a gyroscoplc instrument having a. rotations. bearing arranged. to conduct working fluid which drives the gyro rotor, the present invention is characterised by the fact that a hollow stem through which the working fluid passes, and which is carried by one of the relatively rotatable parts, is surrounded by and rotatable within a washerlike member adapted to bear slidably against the other of said relatively rotatable parts.

According to a further aspect of the invention, he

there is provided a gyroscopic instrument having a rotational bearing including a hollow stem whichconducts working fluid used for driving like member which fits snugly but revolvably upon the stem, and which bears against the said other member with freedom to adjust itself radially relative to said other member.

Preferably; the washer like member is disposed within an annular housing formed in the said other member, the washer-like member conveniently bearing against a shoulder formed in the said other member and being held in position, by a bearing race fitted to said other member.. The bearing race may be larger in diameter than the housing so thatit' bears against'a second shoulder in said other member, the axial separation of the two shoulders being only slightly greater than the axial thicknessof the washer-like member so that when the race is in position the washer-like member has freedom to move radially.

' According to another aspect of the invention there is provided in a. gyroscopic instrument a t bearing comprising in combination a pair of bearing. races, balls between said races, a tubular stem attached to one race and extending through the other race, an annular washer freely rotatable upon'the stem but without substantial freedom, and means for maintaining the washer against the other bearing race, at the same time pe'rmittion with a gyroscopic directionindicator and/the improved bearing may advantageouslyserve for the pivotal mounting'of a drum within a casing in suchan instrument. The stem can conveniently be secured to the casingso as to extendiinto the drum, the washer-like member beingdisposed within a housing formed in the upper wall'ol said drum. p

The inventionisillustrated by way of example n the accompanying diagrammatic dra which; 4 a

Figure iis a. side elevation of'a. gyroscopicdirection indicator shown partly'in section; V

Figure 2 is a fragmentary sectional elevation of the upper part'of the drum andthe correspondi-ng bearing drawn to any enlarged scale; and

Figure 3 is a fragmentary sectional elevation of a detail in Figure 2 drawn to a still. iurthe enlarged scale.

The instrument shown in Figure 1 comprises an outer casing l0 containing a cylindricai closed drum II, which is mounted pivotally within the casing about its vertical axis by means of an upper bearing indicated generally at H and'a' lowerbearing 13. The drum H- is provided-witha circumferential scale ring I which is arranged tobe visible through a front glass, indicated at I15, so as to show the bearing in azimuth of the aircraft or the like to which the casing I0; is secured; The drum ll itself serves as anouter gimbal and'carries. pivotally about a horizontal axis aminner being provided to restore the gimbalirame IE to a, truly horizontal position and hold it so during the. rotational adjustment, of the drum. H details of construction of the upper bearing [2 are shown more. clearly in- Figure 2.. The'wpper walI 20 of the. casing i0. is formed with aniupstanding continuous flange 2| which, together a cylindrical recess formed in the central thickened portion of the upper wall 29 of the drum H and has a tubular portion 30 which fits with clearance within the upper ball race 21. A set of balls, indicated at 3|, are introduced between the two race members 2! and 28 and act to take thrust as well as radial loads.

Fitted into the upper part of the plug member is a stem member having an enlarged upper part 32 and a lower tubular portion 33. The tubular portion 33 extends within a box 34 which is secured to the underside of the wall 29 and which carries a bent tube 35 having a nozzle tube 36 secured to its lower end. The nozzle tube 36 is shaped with a nozzle 3! directed towards the periphery 38 of the gyro rotor 11, the latter being formed with steps or buckets 39 so that air issuing from the nozzle 39 maintains the gyro rotor I! in continuous fast rotation.

To create such a stream. of air through the nozzle 31 air is evacuated'from the casing I 0 through a passageway 40 (see Figure 1), which is conveniently connected with a venturi tube, vacuum pump orother suitable device. more holes (not shown) are formed in the lower wall of the drum ll. Therefore as the casing l 0 is evacuated air from the atmosphere is drawn in through the passage 24, along the centre of the stem member, 32. 33, thence through the tube 35 and nozzle 3! to theinterior of the drum H; from thence it flows through the holes in the bottom and reaches the passage 40. It will be seen that the creation of a partial vacuum within the casing I 0 will also tend to draw air through the stem member 33 and up out of the annular space between the stern member 33 and the lower bearing member 28, said air then passing between the balls 3| into the outer casing l0. This, however, is undesirable partly because it represents a waste of driving energy but more especially because the air always carries minute particles of grit and these become lodged in the lubricant surrounding the balls 3! so thatin course of time the bearing becomes jammed, or at least works stifliy and inefiiciently. In the design of the parts sufilcient clearance must be left between the bearing member 28 and the tubular stem 33 to ensure that there'is no danger of these parts rubbing against one another when the instrument is in operation as this would cause unnecessary friction and would probably spoilthe accuracy of the instrument. Further, the improved means according to the invention are incorporated, as will be seen more clearly in Figure 3. When the lower bearing member 28 is forced into position within the upper wall 29 of the drum l I it is arranged so that the marginal part of its lower plane surface 4! butts against a shoulder '42, thus definitely positioning the bearing member 28. Inwardly of the shoulder 42 the wall 29 is formed with a shallow circular recess, the bottom of which is constituted by a shoulder 43;.said recess serving as an annular housing 44 for a flat washer-like member. 45, conveniently composed of brass or other metal. vThe One or thickness of the member 45 is arranged to be very slightly less than the axial separation of the shoulders 42 and 43 and its outside diameter is appreciably less than the outside diameter of the shoulder 43 so that said member 45 normally has a clearance all round its periphery, as indicated at 46. Its bore 41, however, is a snug but freely rotatable fit upon the'stem member 33, the actual clearance, of course, being considerably less than the clearance 48 between the stem member 33 and the lower bearing bush 28.

It will thus be seen that as'the'outer casing ID with the stem member 33 rotates relative to the ,drum I I any eccentricity of the stern member 33 relative to ,thc'axis of movement will cause the washer 45 to slide radially within the housing 44, this movement being freely permitted by the clearance between the parts. Nevertheless the washer 45 can. rotate freely upon the stem member 33 and yet at all times maintains a substantially air-tight seal'between' said stem member '33 and the lower bearing race 28.

A very slight film of lubricating medium, such as thin oil, on

theparts improves'the air sealing properties of r the device and at the'same time reduces the slight friction still further. v

It'will be understood that the construction which has been described isgiven only by way of example and that various modifications may be made to suit requirements] Thus more than one laterally slidable washer' rnay be used, these conveniently being spaced axially so as to prothe races in bearing engagement therewith, a

hollow stem fixed to one of said members and extending into the-other through the ball races to define a gas conduit coaxial. with the axis of relative rotation of said members, said stem being wholly out of. physical contact with said ball races and defining therewith an annularspace, said other member having an internal annular groove defined'in part by; the respective ball race, and an annular washer in' said groove mounted for free rotation about but in substantially fluid-tight engagement' with said stem, said washer also being axially slidable' on said" stem and being mounted'for free radial movement but restrained, against axial movement in said annular grooveby the respectiveba'll' race, the external diameter of said washer being less than the diameter of saidgroove, whereby the washer may be displaced radially of the axis of relative rotation of said members while maintaining substantially fluid-tight contactswith the stem at all times. a Y I I 2. The mechanism as claimed'in claim '1 fur-v ther comprising, a. shoulder on said other member for maintaining the respective ball race against axial displacement, whereby the load on said bearing means is not transmitted to said Washer. andjthe latter is free to move in said oove.

- DAVID CREW." 

